Adapted from this recipe
Ingredients for dough:
482 grams bread flour
1 tablespoon granulated sugar
2 teaspoons instant yeast or active dry yeast
1 1/4 teaspoons kosher salt
1 cup whole milk
1/2 cup unfed sourdough starter
Ingredients for pretzel boil:
2 quarts water
2 tablespoons baking soda
Ingredients for toppings:
coarse salt
sesame seeds, wheatberries, poppy seeds (optional)
Whisk together flour, salt, sugar and dry yeast in a large bowl. Stir in milk and sourdough starter with a spoon and mix until cohesive dough forms. Knead on a floured surface until smooth (10-15 minutes). Let rise in the bowl until doubled in size (around an hour), covered by a damp towel so it doesn't dry out. Dough may need to rise longer if using active dry yeast.
Cut dough into 8 parts once risen, and roll each part out into a long snake shape, aiming for a resting thickness of about 2 cm or 3/4 of an inch. Thicker rolls may be harder to form into pretzel shapes, but will be pleasingly soft. Thinner rolls are more distinctive looking, but less enjoyable to eat. Twist into pretzel shapes and lay out about four to a cookie sheet. Cover with towels and let rise again until puffy-looking, perhaps 20-30 minutes.
Preheat oven to 400°F.
Boil 2 quarts of water in a non-reactive pan (stainless steel, glass, etc.). Add baking soda before the water reaches a boil. Reduce temperature so the water is simmering, and submerge each pretzel in the water, cooking for about 45 seconds per side. Remove with a slotted spoon and place on parchment-paper'd baking sheets, about four to a sheet. Sprinkle with coarse salt before the dough dries.
Bake pretzels until at least golden brown. Pretzels can become quite dark brown without problems, and darker pretzels have a stronger flavor and chewier crust. Baking time is 18-25 minutes depending on your oven and how brown you want your pretzels. Despite initially thinking golden was better than dark brown, I have found the darker pretzels more pleasing.
Let stand for 5-10 minutes to cool, and serve warm. Pretzels are excellent alone, but go very well with mustard, cream cheese, smoked salmon, etc. Pretzels can be stored in a non-airtight container for about a day, but they degrade quickly and are best eaten fresh.